Sybaris on the Traeis was an ancient city situated on the Traeis river, now known as the Trionto. It shares its name with the original city of Sybaris (Ancient Greek: Σύβαρις) which was destroyed in 510 BC. Its former inhabitants built a new city, Thurii, not far from the site of Sybaris. This new colony was founded together with other Greek settlers in 446/445 BC. Soon a conflict arose between the two groups and most of the Sybarites were killed by the other Greek colonists of Thurii. The Sybarites who managed to flee then founded Sybaris on the Traeis a short time after 444 BC. The city was destroyed by the Bruttii not long after their emergence as an ethnic group in 356/355 BC.
In the present day the Trionto river flows through the Province of Cosenza in Calabria, Italy. The mouth of the river lies approximately 25 kilometers southeast of the site of Thurii. The exact location of Sybaris on the Traeis has not been found along the course of the Trionto yet.